Design of Two-Degree-Of-Freedom (2DOF) Steering Control for Automated Guided Vehicle

Automated Guided Vehicles (AGV) exhibit serious instability in its steering mechanisms, in most cases this results in “snaking” or wavering movement of the vehicle as the speed rises above 5m/s. In order to solve this problem, the steering controller needs to be able to address the two main objective of control, the first one is the set-point tracking and the other one is load disturbance rejection. However, these two aspects conflict with each other practically and cannot be accomplished by the conventional one degree of freedom (1DOF) PID controller. This problem was solved through the use of a two degree of freedom (2DOF) PID controller. The 3-wheels AGV used in this project is modeled using the two-wheel bicycle model to develop the transfer function. The project design work is carried out on Windows 7 platform with MATLAB R2009a software application. This platform was chosen as the version of the application contains the necessary toolboxes to quickly and stably run the necessary simulations. The control strategies was developed and simulated in the SIMULINK environment using the Control Toolbox, and the controller action was viewed, fine-tuned and verified using the PID tuner utility because it provides the capability to carry out auto-tuning of the controller as desired without the rigors involved in manual controller tuning. The simulated result showed great improvement in the final AGV steering controller action in the Rise Time and Settling Time less than 1 second, and overshoot less than 2% of the final value. The control strategies promoted in this work are reference tracking and disturbance rejection. This research will help to stimulate advancement into further development of suitable steering controllers of Automated Guided Vehicles and promote usage in our local industry.